Drop-out process for halftone photography



April 24, 1962 A. L. HUTTKAY DROP-OUT PROCESS FOR HALFTONE PHOTOGRAPHYv Filed June 5, 1959 United States Patent O "ice 3,031,303 DROP-OUT PROCESS FOR HALF'I'ONE PHOTGRAPHY Arthur L. Huttkay, Oakwood Road E., Watchung, NJ. Filed June 3, 1959, Ser. No. 817,755 4 Claims. (Cl. 96-45) :I'his invention deals with a new process for preparing printing plates. More particularly, it relates to a process for producing drop-out halftone negatives and positives by eliminating all halftone screening dots in the background or highlight sections of halftone negatives and positives. c This process is particularly adaptable for making printing plates used in letterpress, offset and other types of prlnting-employing a glass screen or contact screen, to obtain a halftone negative or positive by use of screen ruling ranging from 50 lines to any fine screen rulings (i.e., for newspaper printing, magazine printing or offset printing).

In preparing printing plates, it is necessary for this plate to have a proper size dot in the highest tone area, represented by the art work (Wash drawing), this dot size for printing and staple purposes must be what is known in the printing and engraving field as a 10% dot, which represents a highlight dot. This percent of dot is necessary, regardless of the lightest shade in a given piece of art work, which in 99% of cases is at less than 5% gray or is vignetted olf into paper, not visible to the eye. Art work of this type cannot be automatically dropped-out, and shades lighter than a shade will be `dropped out, as though they were white, thereby producing an inferior yand untrue facsimile of the art work. Artists, when preparing their art work, in most cases, are ignorant of this fact, hence, it is necessary to increase the tones of the drawing in some manner, since the dropout technique itself usually effects some loss in tonal quality of the wash drawing.

In the past, drop-out halftones have been processed, without intensification, by hand, which generally took up four hours of painstaking masking and opaquing work per newspaper page. In recent years, this amount of time has been reduced by the use of iiuorescent pigments wherein special ultraviolet light techniques are employed. Subsequently, the processing was further simplified by use of an intensiiication process wherein the wash water for the art work is blended with chemicals which are then reacted with other chemicals to intensify the washed (painted) portion with a bright color, such as yellow, said color preserving a high enough shade intensity in the washed portion `during drop-out operations. Although the latter process has effected saving in time and effort, it has been subject to a number of faults, the chief among which are mutilation of the original drawing, lack of good detail, and the necessity of using special exposure equipment not always available.

One purpose of the present invention is to insure unfailing reproduction of art work, regardless of the tonal shading technique used by the artist. Other purposes include assurance of returning the original drawing in its original or almost original condition, improved detail in reproduction, easier working and washing of the original drawing, and elimination of the need for special exposure equipment.

Briefly, the present invention comprises use of a water-soluble thiocyanate in the water used with the pigment in preparing the original wash drawing. After the drawing is completed, the thiocyanate-treated portion is intensified by a spray of aqueous copper solution, whereby copper thiocyanate is formed, and the intensied drawing is exposed through the screen with white (arc) light. When the screened (halftone) exposure is com- 3,03 l ,3 03 Patented Apr. k24, 1962 plete, the screen is removed and, while in the same position, the film is given another exposure through a sandwich filter of light blue and yellow, whereby a superior drop-out halftone negative is produced.

It should be noted here that throughout this specification and claims the term highlight sections is used to designate those sections of an illustration or drawing which are required to be printed in reproduction, as pure white, i.e., free from any screen pattern, and is usually used as referring to background or white sections of an illustration. The term tone sections refers to the shaded or dark sections of the original illustration or drawing to be printed in reproduction as halftones. Also, the term negative is used to designate photographic reproductions on any type of photographic material in which the highlight sections of the original illustrations or drawing appear opaque, the tone sections being more or less transparent or white. In the same manner, the term positive designates photographic reproduction on any kind of photographic material, i.e., on photographic paper, film or plate, in which the highlight sections of the original drawing are substantially white or transparent, the tone Values of the tone sections being substantially the same as on the original drawing.

Finally, the term wash drawing as used herein should not be limited to the exact meaning of the word, but the term is intended to include other types of illustrations, eg., photographic or otherwise, if they are combined with a white background, and art work is done thereon with an aqueous pigmented medium.

The invention will be understood more clearly by reference to the accompanying drawing depicting a preferred embodiment. In this drawing, FIGURE 1 illustrates a type of original wash drawing in which the tone section disposed in the center of the highlight section has been applied with pigmented aqueous thiocyanate solution. FIGURE 2 represents the same drawing with the tone section intensified by spraying with aqueous copper solution. FIGURE 3 depicts the drawing of FIGURE 2 as viewed through the screen in the production of a halftone, the screen being the cause of the dots in the highlight section (to be removed). FIGURE 4 illustrates `a drop-out negative obtained after removal of the screen and exposure of the film through the sandwich filter, while FIGURE 5 is a drop-out positive, print or plate produced from the negative of FIGURE 4. FIG- URE 6 illustrates the drawing of FIGURE 2 after being sprayed with clearing solution.

The process may be described in detail, while referring to the drawing, as follows:

ln the water (wash) employed for liquefying the pigment in the preparation of the wash drawing of FIGURE 1, there is added a water-soluble thiocyanate, as, for example, to 16 ounces of water used, there may be added 2 ounces of potassium thiocyanate, 20 grains of a water softener, such as bor-ax, and 16 drops of aqua ammonia, which serves as a pigment solvent or ernulsiiier, and also serves as a pigment flow controller. This solution is employed in liquefying the pigment in the preparation of the tone section l disposed within the highlight section 2 of the wash drawing of FIGURE l.

After drying, the tone section 1 (FIGURE 1) of the wash drawing is sprayed with an aqueous solution of a copper salt, such as copper sulfate, the concentration thereof depending upon the depth of tone desired. First, itis preferable to prepare a stock solution of say 3 ounces of crystalline copper sulfate (CUSO4-5H2O) per 32 ounces of water. A working (spray) solution then may be prepared lby dilution of the stock solution with water, the dilution depending upon the tone desired in the sprayed drawing. Assuming the use of 20% tone (10% deeper than that of section l which is assumed to be of l% value), is desired, section or area 1 of FIGURE 1 is sprayed with a solution containing about 8 drams of the stock solution per 16 ounces of water. When this latter working solution is applied to the thiocyanated wash drawing in the form of a tine spray, a deepening or intensification of tone is immediately observed, the sprayed area 1a having a darker tint, or 20% tone, which does not ciect seriously the returnability of the wash drawing of FIGURE 2.

Thereafter, the drawing of FIGURE 2 is exposed for photographing `by white (arc) light (its appearance through the screen being somewhat like the representation in FIGURE 3, the light tone area 3 being the screen background to be dropped-out). The basic exposure conditions employed in this step are the same as those used in other or conventional processes in the production of halftone negatives.

Thereafter, the screen is removed, and the exposed lm (having been previously taped down or held by vacuum with the art work so as to remain in the same position) is given another exposure, using two lters sandwiched together, a light blue (e.g., Wrattan 44A), and a yellow (e.g., K2) for about 5 to 10 seconds. This effects the drop-out without affecting excessively the tone section, so that a negative is obtained as in FIGURE 4, the dropout area 4 being black, while the tone section 5 is in halftone with a tone value of about 80-90%. From this negative, a postive or plate such as that depicted in FIG- URE 5, is obtainable, the tone section 1b being in halftone with a tonal value close to that of section 1 of the original wash drawing of FIGURE 1, and with highlight section 2 free of any dots which would otherwise be present due to use ofthe screen 3 (FIG. 3).

If it is desired to remove the intensifying chemical from the wash drawing of FIGURE 2, this is readily accomplished by spraying the tone section 1a with a clearing solution comprising an aqueous solution of thiourea (thiocarbamide), preferably in the concentration of l ounce of the chemical to 16 ounces of water. It must be emphasized here, however, that the drawing of FIG- URE 2 is in returnable condition even without the clearing step, in spite of the fact that it may be of slightly deeper tone than section 1 in FIGURE 1. Drawings obtained by conventional intensifying processes, however, apply a highly objectionable color, e.g., a strong yellow shade, in the tone sections. Since this color is hard to remove, it is diiicult for the artist to work over said intensied drawing if correction or addition of art work is needed to remake the plate.

As mentioned previously, the wash water additive used on the drawing of FIGURE 1 is a water soluble thiocyanate, such as an alkali metal thiocyanate, and more particularly, a thiocyanate of sodium, potassium or ammonium, or mixtures thereof. Since the latter is colorless, it has no effect upon the tone, and it is used prefera-bly in an amount of 2 to 10 ounces per 16 ounces of water. Although the thiocyanate may be employed in the water alone, it has been found desirable to add a small amount (5 to 50 grains per 16 ounces) of a water softener, such as borax, to insure high quality. Also,

the small amount of ammonia (16 to 25 drops per 16 ounces), or other pigment emulsifier or softener, aids in controlling pigment flow during the painting (washing) of the drawing, making it superior to water in this respect.

The intensier to be applied by spraying in a tine spray over the additive-washed drawing, to prepare the intensiied drawing of FIGURE 2, is an aqueous solution of a copper salt, such as copper sulfate, copper nitrate, copper ammonium sulfate, etc., the increase in tonal quality of the thiocyanated drawing being determined by the concentration of the copper solution sprayed upon the tone section. For example, the following table will give a rough idea of the tone increase obtained, using said copper sulfate stock solution in the concentrations specilied, per 16 ounces of water.

Stock solution,

Percent tone: drams Iclaim:

1. A process for producing a drop-out halftone positive of a wash drawing having tone and highlight sections, comprising applying to the tone sections of said drawing a water-soluble thiocyanate, thereafter treating said tone sections with an aqueous copper solution whereby tonal value is increased, making a negative 'by exposure of said drawing through a screen in presence of white light, then in the same position, to light passing through a combination of light blue and yellow filters in the absence of said screen, whereupon drop-out occurs only in the highlight sections, and preparing a positive `from said negative.

2. A process according to claim 1 in which the watersoluble thiocyanate is a thiocyanate of an alkali metal.

3. A process according to claim 1 in which the concentration of thiocyanate and copper solutions applied increase the tonal value of said tone section by at least 10%.

4. A process according to claim 1 in which the tonal value of the tone sections in the thiocyanate and coppertreated drawing is reduced to its original value by treating said treated tone sections with an aqueous solution of thiourea.

References Cited in the file of this patent UNITED STATES PATENTS 1,581,012 Philippe et al. Apr. 13, 1926 2,315,101 Zukrnann Mar. 30, 1943 2,362,826 Huttkay NOV. 14, 1944 OTHER REFERENCES Clerc: Photography, Theory and Practice, 2 ed., 1937, Isaac Pitman and Sons Ltd., New York. Pages 3124313. 

1. A PROCESS FOR PRODUCING A DROP-OUT HALFTONE POSITIVE OF A WASH DRAWING HAVING TONE AND HIGHLIGHT SECTIONS, COMPRISING APPLYING TO THE TONE SECTIONS OF SAID DRAWING A WATER-SOLUBLE THIOCYANATE, THEREAFTER TREATING SAID TONE SECTIONS WITH AN AQUEOUS COPPER SOLUTION WHEREBY TONAL VALUE IS INCREASED, MAKING A NEGATIVE BY EXPOSURE OF SAID DRAWING THROUGH A SCREEN IN PRESENCE OF WHITE LIGHT, THEN IN THE SAME POSITION, TO LIGHT PASSING THROUGH A COMBINATION OF LIGHT BLUE AND YELLOW FILTERS IN THE ABSENCE OF SAID SCREEN, WHEREUPON DROP-OUT OCCURS ONLY IN THE HIGHLIGHT SECTIONS, AND PREPARING A POSITIVE FROM SAID NEGATIVE. 